Carbon nanofiber-based hydrodesulfurization catalyst with molybdenum oxide and cobalt oxide

ABSTRACT

Carbon nanofiber doped alumina (Al—CNF) supported MoCo catalysts in hydrodesulfurization (HDS), and/or boron doping, e.g., up to 5 wt % of total catalyst weight, can improve catalytic efficiency. Al-CNF-supported MoCo catalysts, (Al-CNF-MoCo), can reduce the sulfur concentration in fuel, esp. liquid fuel, to below the required limit in a 6 h reaction time. Thus, Al-CNF-MoCo has a higher catalytic activity than Al-MoCo, which may be explained by higher mesoporous surface area and better dispersion of MoCo metals on the AlCNF support relative to alumina support. The BET surface area of Al-MoCo may be 75% less than Al-CNF-MoCo, e.g., 166 vs. 200 m 2 /g. SEM images indicate that the catalyst nanoparticles can be evenly distributed on the surface of the CNF. The surface area of the AlMoCoB5% may be 206 m 2 /g, which is higher than AlMoCoB0% and AlMoCoB2%, and AlMoCoB5% has the highest HDS activity, removing more than 98% sulfur and below allowed levels.

BACKGROUND OF THE INVENTION Field of the Invention

This application relates to hydrodesulfurization and catalysts useful inhydrodesulfurization.

Description of the Related Art

Diesel, oil, gasoline, and other unrefined or at least partially refinedproducts usually contain a considerable amount of sulfur-containingcompounds that generate SO_(x) gases. These gases pollute theenvironment and lead to human health problems. From the petrochemicalpoint of view, SO_(x) gases reduce the efficiency of plant units andcause corrosion to reactors, pipes, storage vessels, and export vessels.Stricter environmental regulations have moved the oil industry tominimize sulfur content in refinery products and thereby meet new fossilfuel quality standards.

Various approaches to reducing sulfur content in crude oil and itsfractions, such as gasoline, diesel, and jet fuel, includehydrodesulfurization (HDS), extractive desulfurization (EDS), oxidativedesulfurization (ODS), adsorptive desulfurization (ADS) andbiodesulfurization (BDS). HDS involves reacting fluid or fluidized fuelwith a hydrogen stream over heterogeneous catalyst at high temperaturesand pressures. EDS involves mixing fuels with suitable solvents andsubsequently separating to extract the organosulfur species. ADS avoidshigh temperatures and removes organosulfur compounds by physicalabsorption on the surface/matrix of adsorbent material(s). ODS involvesoxidizing organosulfur compounds with oxidant(s) and subsequentlyseparating resulting sulfoxide(s) and/or sulfone(s) by solventextraction. BDS employs microorganisms with an inherent capacity totransform and/or utilize organosulfur compound(s), especially throughmetabolism.

HDS is the most used of the above techniques in oil refining due to itsrelative effectiveness and practicality. However, HDS efficiency dependson the performance and stability of the catalyst(s) used. Academic andindustrial communities have sought to develop new catalysts and improveavailable catalysts to ensure the effective desulfurization and conformwith the mandated minimum levels.

A great deal of research in the field of heterogeneous catalysis hasbeen devoted to the hydrodesulfurization of liquid fuels. Transportationfuels are major sources of SO₂, an air pollutant and cause of acid rain,which has led to regulations restricting sulfur emissions into theatmosphere from fuel consumption. Hydrotreating to remove sulfur fromdiesel or gasoline is important in any petrochemical plant. Ultra-cleanfuel standards with respect to sulfur continually increase, for example,sulfur contents in diesel fuel in Europe can be no more than 10 ppmsince 2009 and 15 ppm in the US since 2006.

Producing ultra-low sulfur gas oil at affordable costs requiresdeveloping and upgrading existing process technologies, including thecatalysts used. Research has focused on new hydrotreating catalysts witha higher activity for HDS. Conventional HDS catalysts use nanometricMoS₂ crystallites with cobalt or nickel oxides supported ongamma-alumina, i.e., γ-Al₂O₃. Catalysts having an active phase with Moor MoS₂, promoted with Ni or Co, supported on γ-Al₂O₃, are used widelyfor HDS in oil refineries.

The catalyst support can play a critical role in the stability andperformance of catalysts used in HDS by providing surface area foractive site dispersal. Research into enhancing HDS catalyst performancehas included, for example, controlling promoters, tuning active phaseand tailoring the structure of supports. Novel support(s) and/or dopantsgained interest because HDS performance correlates to thephysicochemical nature of the support as well as the active phase.

Supports can contribute to HDS catalytic efficacy through texturaland/or acid-base properties which can be superior to those of simpleoxides. Various materials have been investigated as HDS catalystsupports, including alumina (e.g., α-Al₂O₃, and γ-Al₂O₃), zeolites,carbon structures, nanoporous carbon, mesoporous carbon, zirconia(ZrO₂), titania (TiO₂), and silica (SiO₂). Presently, γ-Al₂O₃ is themost widely used support material for HDS catalysts because of itsmechanical strength and ability to impart stability to the catalystunder normally harsh HDS reaction conditions. Alumina normally has highsurface area and good porosity and its structure generally includesacidic sites. However, alumina may interact strongly with certaintransition metal oxides, potentially impede complete sulfidation,ultimately reducing the HDS catalyst performance.

Still, the most widely used support for hydro-refining catalysts isγ-Al₂O₃ due to its appealing mechanical properties, inherent acid-basefeatures, and adjustable surface physicochemical properties.Conventional alumina has textural porosity with low surface area (<250m²/g) and widely dispersed pore size, which may constrain its catalyticactivity. The structure of α-Al₂O₃ may be relevant to developing viablespecies for HDS, though γ-Al₂O₃ in many cases provides higher surfacearea, e.g., for loading active catalyst, such as W, Ni, Mo and/or Conanoparticles in the case of HDS.

Modification of sol-gel Al₂O₃ support with boron at various ratiosduring the sol-gel synthesis conventionally shows that theboron-to-aluminum (B:Al) ratio affects the structure and properties ofthe sol-gel prepared B—Al₂O₃ powders, and that the catalytic performanceof catalysts prepared on the B—Al₂O₃ powders may depend on the B/Alratio. In particular, an increase in the acidity of the Al₂O₃ by theintroduction of B may improve the HDS properties of the catalysts.

US 2017/0369792 A1 by Yamani, et al., discloses a process for producingan unsupported molybdenum sulfide nanocatalyst comprising atomizing amolybdenum oxide solution to form a molybdenum oxide aerosol, pyrolyzingthe molybdenum oxide aerosol with a laser beam to form the unsupportedmolybdenum-based nanocatalyst, and pre-sulfiding at least a portion ofthe unsupported molybdenum-based nanocatalyst to form an unsupportedmolybdenum sulfide nanocatalyst, wherein the unsupportedmolybdenum-based nanocatalyst, the unsupported molybdenum sulfidecatalyst or both are in the form of nanoparticles with a diameter of 1to 10 nm and in a distorted rutile crystalline structure. Yamani alsodiscloses a method of selective deep hydrodesulfurization whereby ahydrocarbon feedstock having at least one sulfur-containing componentand at least one hydrocarbon is contacted with the unsupportedmolybdenum sulfide nanocatalyst.

As noted, Yamani requires an unsupported catalyst. Yamani disclosesneither a boron nor carbon nanofiber-modified molybdenum-cobalt catalystsupported on alumina, instead focusing on unsupported molybdenum and/ormixed metal (i.e., Mo, W, Co, and/or Ni) sulfide catalysts forhydrodesulfurization reactions.

CN 106268976 A by Li, et al., discloses a gasoline selectivehydrodesulfurization catalyst, its make, and use. The total mass of thecatalyst being 100%, Li's catalyst is prepared from 3 to 15 wt % of VIIIgroup metal, 45 to 58 wt % of Mo, and 35 to 40 wt % of S. A preparationmethod of the catalyst comprises the following steps: 1, a defect-richmolybdenum disulfide nanosheet precursor with a non-stoichiometric ratiois prepared; 2, one kind of VIII group metal is added into themolybdenum disulfide nanosheet precursor through an ultrasonic assistingdipping method, the molar ratio of the VIII group metal to Mo is (0.1 to0.5):1, the specific surface area of the molybdenum disulfide nanosheetprecursor ranges from 40 m²/g to 90 m²/g, the pore volume ranges from0.1 mL/g to 0.25 mL/g, and the molar ratio of sulfur to molybdenum is(1.92 to 2.10):1. Li prepares defect-rich molybdenum disulfide bycontrolling the stoichiometric ratio of molybdenum disulfide, andexposing more active loci.

While Li teaches a hydrodesulfurization catalyst, Li's catalyst requires35 to 40 wt % of sulfur, and 45-58 wt % of Mo, and forms a defect-richmolybdenum sulfide with a specific surface area 40 to 90 m²/g. Li'scatalyst uses 3 to 15 wt % of Group VIII group metal, which may beeither Co or Ni. Li only describes supports in its background andcomparative examples, apparently avoiding these and at least failing todescribe supports for its invention, much less point to using an aluminasupport, modified or not. Li discloses neither a boron nor carbonnanofiber-modified molybdenum-cobalt catalyst supported on alumina.

MX PA 02012764 A by Toledo discloses a procedure for preparingmolybdenum and tungsten disulfide nanotubes with an inorganicfullerenes-type structure for desulfurization from gasolines, diesel, orheavy hydrocarbons. Toledo's nanotubes include molybdenum disulfide ormolybdenum tungsten, with stacking levels of 1 to 20 layers bound toeach other by weak Van der Waals-type bonds, with a separation of 0.6 nmbetween layers and with lengths from 1 to 50 μm. Toledo's nanotubes haveopen ends and an internal diameter of 1 to 15 nm, with curved areashaving catalytically active sites for hydrocarbon HDS reactions in theexterior and interior of the nanotubes.

While Toledo's catalysts are useful for hydrodesulfurization, itscatalysts require tungsten and have specific surface areas of no morethan 100 m²/g. Moreover, Toledo does not contain nanostructures ofcarbon, but instead inorganic nanostructures. Toledo does not disclosedoping with boron, and apparently fails to teach the use of an aluminasupport. Toledo discloses neither a boron nor carbon nanofiber-modifiedmolybdenum-cobalt catalyst supported on alumina.

U.S. Pat. No. 9,259,728 to Kim, et al., disclose a catalyst having metalcatalyst nanoparticles supported on natural cellulose fibers and amethod of preparing the same, whereby natural cellulose fibers aresubjected to specific pretreatment to increase a surface area and formdefects on the surface thereof and metal catalyst nanoparticles are thensupported on the cellulose catalyst support in a highly dispersed state,thereby providing improved catalysis while allowing production of thecatalyst at low cost. The catalyst may be utilized for various catalyticreactions.

Kim indicates that cellulose is required. In addition, Kim requiresneither Mo nor Co, nor an alumina support. Kim describes metal catalystnanoparticles on cellulose including platinum, nickel, cobalt, andmolybdenum, but not a combination of molybdeum and cobalt particularly.Kim does not mention carbon nanofibers or boron additives. Moreover, Kimdoes not disclose a boron or carbon nanofiber-modified molybdenum-cobaltcatalyst supported on alumina.

CN 101890379 B by Wang, et al., discloses a bulk phase catalyst and itspreparation. Wang's bulk phase catalyst is prepared from an inorganicoxide precursor, a hydroxide gel and an active metal hydroxide gelserving as raw materials by molding and roasting. Wang's bulk phasecatalyst may be prepared from a hydroxide gel containing a surfactantand hydrocarbon components, which, after the hydroxide gel is molded androasted, forms nano oxide particles by dehydrating the polymerizedhydroxide. Wang's nano oxide particles have a rod-shaped basic structureand pile up into a framework structure in an unordered mode.

Wang may employ boron or phosphorous in its invention, but Wang has noparticular teaching on metals useful, nor carbon nanofibers, nor thespecific use of alumina. Wang allows the use of Ni, Co, Mo, W, Cu, Zn,Cr, Fe, Mn, Pt, or Ru, and exemplifies only singular metals, primarilyNi. Wang describes alumina, silica, titania, zirconia, lanthanum oxide,magnesia, or calcium oxide as supports, but appears to focus onnanostructured hydroxides. Wang discloses neither boron nor carbonnanofiber-modified molybdenum-cobalt catalyst, nor one supported onalumina.

Zhang et al.'s in J. Nat. Gas Chem. 2008, 17(2), 165-170, disclosescarbon nanotubes supported Co-Mo catalysts (Co-Mo/CNTs) for selectivehydrodesulfurization (HDS) of fluid catalytic cracking (FCC) gasoline,studies are carried out using in situ Fourier transform infraredspectroscopy (FT-IR). Zhang 2008 evaluates catalytic performances ofCo-Mo/CNTs catalysts with a mixture of cyclohexane, diisobutylene,cyclohexene, 1-octene (60:30:5:5, volume ratio) and thiophene (0.5%,ratio of total weight) as model compounds to simulate FCC gasoline.Zhang I's HDS experimental results suggested that the HDS activity andselectivity of Co-Mo/CNTs catalysts were affected by Co/Mo ratio, thatthe optimal Co/Mo atomic ratio is about 0.4, and that the optimumreaction temperature is 260° C. Zhang I's in situ FT-IR studies revealedthat 1-octene can be completely saturated at 200° C. Zhang I's FT-IRresults indicate that thiophene HDS reaction occurred mainly throughdirect hydrogenolysis route, whereas thiophene HDS and diisobutylenehydrogenation reaction over Co-Mo/CNTs catalysts might occur on twodifferent kinds of active sites.

Thus, Zhang 2008 relates to HDS and uses an MoCo catalysts modified withcarbon nanotubes, rather than carbon nanofibers, i.e., Zhang I's carbonnanostructures are hollow. However, Zhang does not indicate usingalumina as a support and instead impugns alumina as not useful,particularly in China or with hydrocarbon streams having more than 15%olefins, such as 40 to 50% in Chinese sources. Zhang 2008 states thatthe HDS activity and selectivity of Co—Mo/CNTs catalysts are higher thanthose of traditional ones under the same reaction conditions, such asCo—Mo/Al₂O₃ and Co-Mo/activated carbon catalysts. Moreover, Zhang 2008fails to disclose a boron-modified molybdenum-cobalt catalyst, nor acarbon nanofiber-modified molybdenum-cobalt catalyst supported onalumina.

Zhang et al. in Basic Solid State Physics 2009, 246 (11-12), 2502-2506,discloses commercial carbon nanotubes (CNTs) in two heterogeneouslycatalyzed reactions, i.e., NH₃ decomposition and oxidativedehydrogenation of ethylbenzene (EB). For NH₃ decomposition, CNTs wereused as supports for Co-Mo nanoparticles. The structure of fresh andused catalysts was characterized by X-ray diffraction (XRD),high-resolution transmission electron microscopy (HRTEM) and line-scanenergy dispersive X-ray (EDX). Most of the nanoparticles areindividually separated and the synergism mainly increases the long-termstability rather than the activity. For oxidative dehydrogenation, themetal-free CNTs display a superior performance as compared to theFe-doped CNTs.

Zhang 2009 discloses using an MoCo catalyst in different reactions fromHDS—NH₃ decomposition and oxidative dehydrogenation, and uses nanotubes,rather than nanofibers. Zhang 2009 appears to avoid alumina, and doesnot include any boron doping. Instead, Zhang 2009 has Fe-doping of itscarbon nanotube support. Zhang 2009 does not disclose a boron or carbonnanofiber-modified molybdenum-cobalt catalyst supported on alumina.

Further recent investigations have focused on nanofilamentous carbons(NC), such as carbon nanofibers (CNF), fullerenes, and carbon nanotubes,as a catalyst support in the HDS. These studies mostly use Ni and/or Moas active metals, rather than the combination of MoCo, and usuallyexclude alumina.

Thus, new catalysts combining high surface areas of NC with themechanical strength of alumina, optionally or alternatively usingcertain dopants or additives, to improve alumina-based catalysts, couldpresent worthy targets for HDS catalyst development.

SUMMARY OF THE INVENTION

Aspects of the invention provide catalysts, particularlyhydrodesulfurization catalysts, comprising: catalytic materialcomprising molybdenum and cobalt, optionally as nanoparticles ofmolybdenum and/or cobalt; and a catalyst support comprising alumina; and(i) wherein the catalyst support further comprises carbon nanofibersdispersed on a surface of the alumina, and/or (ii) wherein the catalystfurther comprises a dopant comprising boron, wherein the catalyticmaterial is homogenously dispersed on the catalyst support. Thesecatalysts may be optionally modified with any permutation of thefollowing features.

The dopant comprising the boron may be present in a range of from 1 to5.5 wt % relative to total catalyst weight.

The catalytic material may comprise 12 to 18 wt % of molybdenum,relative to the total catalyst weight, and/or 3 to 8 wt % of cobalt.

BET surface areas of catalysts within the scope of the invention may bein a range of from 150 to 230 m²/g.

The carbon nanofibers may have an average diameter of 20 to 40 μm.

Catalysts of the invention may have meso-pore surface areas in a rangeof from 165 to 185 m²/g, total pore volumes in a range of from 0.3 to0.33 cm³/g, average pore diameters in a range of from 5 to 7 nm, and/orhierarchy factors in a range of from 0.02 to 0.035.

The catalytic material may comprise no more than 5 wt % of any of Wand/or Ni, or even no more than 5 wt % of any metal besides Mo and Co,and/or no more than 5 wt % of sulfur, outside of operational conditions.

Aspects of the invention provide methods of hydrodesulfurizing a firstmixture comprising an organosulfur, the method comprising: contactingthe first mixture with any catalyst(s) within the scope of the inventionin the presence of hydrogen gas, thereby forming a second mixturecomprising less sulfur than the first mixture, wherein the contacting iscarried out at a temperature in a range of from 250 to 350° C. for up to6 hours and a hydrogen gas partial pressure in a range of from 50 to 60bar-a. Inventive methods may be ones in which the first mixture iscontacted with the hydrogen gas for 5 to 6 hours, and a ratio of anorganosulfur concentration in the second mixture to the organosulfurconcentration in the first mixture is in a range of from 1:10 to 1:1000.

Aspects of the invention provide reactor systems, comprising: a vesselwith an internal cavity that contains inventive catalyst(s) as describedherein, wherein the vessel comprises (a) a hydrogen inlet configured todeliver hydrogen gas to the internal cavity, and (b)a feed inletconfigured to deliver a sulfur-containing mixture to the internalcavity; a stirrer configured to stir the catalyst and thesulfur-containing mixture in the presence of the hydrogen gas; a firststorage tank located upstream of the vessel and fluidly connected to thehydrogen inlet, wherein the first storage tank delivers the hydrogen gasto the hydrogen inlet; and a second storage tank located upstream of thevessel and fluidly connected to the feed inlet, wherein the secondstorage tank delivers the sulfur-containing mixture to the feed inlet,wherein the sulfur-containing mixture is contacted with the catalyst inthe presence of the hydrogen gas to form a desulfurized mixture.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 shows a pictorial of synthetic steps useful in preparing certainAl—CNF—MoCo catalysts within the scope of the invention;

FIG. 2A and B show the N₂ adsorption and desorption isotherm (a) and thepore size distribution (b) of Al—CNF—MoCo and Al—MoCo catalysts asdescribed in Example 1;

FIG. 3 shows the H₂-TPR profiles of (a) the Al—MoCo catalyst and (b) theAl—MoCo—CNF catalyst prepared as described Example 1;

FIG. 4 shows the XRD patterns of (1) the Al—MoCo catalyst, (b) CNFalone, and (c) the Al—CNF—MoCo catalyst prepared as described Example 1;

FIG. 5A to D show SEM images at various scales (a, b, c) to theAl—CNF—MoCo catalyst prepared as described Example 1 and (d) thecorresponding EDX spectrum;

FIG. 6 shows the FT-IR spectra of the Al—MoCo catalyst and theAl—MoCo—CNF catalyst prepared as described Example 1;

FIG. 7 shows the TGA curves of the Al—MoCo catalyst and the Al—MoCo—CNFcatalyst prepared as described Example 1;

FIG. 8 shows the sulfur concentration over time for HDS reactions usingthe Al—MoCo catalyst and the Al—MoCo—CNF catalyst as described Example 1using an initial sulfur concentration 550 ppm, a reaction temperature of300° C., an H₂ partial pressure of 55 bar, and stirring at 180 rpm;

FIG. 9 shows possible pathways for the HDS of DBT at 300° C. in thepresence of the Al—MoCo catalyst and the Al—MoCo—CNF catalyst preparedas described Example 1;

FIG. 10A to C show (a) a gas chromatogram of HDS of DBT over theAl—MoCo—CNF catalyst prepared as described Example 1, (b) the GC-MSspectrum of fragments corresponding to biphenyl HDS product, and (c) theGC-MS spectrum of fragments corresponding to the bicyclohexyl HDSproduct;

FIG. 11A and B show HDS reaction process designs suitable for practicingaspects of the invention;

FIG. 12 shows an alternate HDS reaction process design, including arecycle system, suitable for practicing aspects of the invention;

FIG. 13 shows a pictorial of synthetic steps useful in preparingboron-modified Al—MoCo catalysts, AlMoCoB0%, AlMoCoB2%, and AlMoCoB5%,within the scope of the invention;

FIG. 14 shows a schematic diagram of the reaction system layout for HDSreactions conducted in Example 2;

FIG. 15 shows BET surface area plots for (a) the AlMoCoB0% catalyst, (b)the AlMoCoB2% catalyst, and (c) the AlMoCoB5% catalyst as described inExample 2;

FIG. 16A and B show (a) the H₂-TPR results, and (b) NH₃-TPD results, ofthe boron-modified HDS catalysts described in Example 2;

FIG. 17A to C show XRD patterns of the boron-modified HDS catalystsdescribed in Example 2, i.e., (a) AlMoCoB0%, (b) AlMoCoB2%, and (c)AlMoCoB5%;

FIG. 18 shows FT-IR spectra of the boron-modified HDS catalystsdescribed in Example 2, i.e., (a) AlMoCoB0%, (b) AlMoCoB2%, and (c)AlMoCoB5%;

FIG. 19A to F show (a) an energy-dispersive X-ray (EDX) spectrum with anelemental analysis table of AlMoCoB0%, (b) an SEM image of AlMoCoB0%,(c) an EDX spectrum with an elemental analysis table of AlMoCoB2%, (d)an SEM image of AlMoCoB2%, (e) an EDX spectrum with an elementalanalysis table of AlMoCoB5%, (f) an SEM image of AlMoCoB5%;

FIG. 20 shows TGA graphs of the boron-modified HDS catalysts describedin Example 2, i.e., (a) AlMoCoB0%, (b) AlMoCoB2%, and (c) AlMoCoB5%;

FIG. 21A and B show (a) normal plots of effects, and (b) interactionplots, of the boron-modified HDS catalysts;

FIG. 22 shows a shows a chart of comparative catalytic performance ofthe boron-modified catalysts, i.e., AlMoCoB0%, AlMoCoB2%, and AlMoCoB5%,at different HDS reaction intervals under an initial concentration of650 ppm BDT at a reaction temperature of 300° C., at 50 bar H₂ partialpressure, stirring at 150 rpm;

FIG. 23 shows an alternative, simplified presentation of reactionpathways for hydrodesulfurization of dibenzothiophene; and

FIG. 24A to D show (a) a GC-MS chromatogram of reaction products of anHDS reaction of BDT in decalin in the present of the boron-modifiedcatalysts from Example 2, (b) a GC-MS spectrum of the DBT startingmaterial, (c) a GC-MS spectrum of the biphenyl HDS product, and (d) aGC-MS spectrum of the cyclohexylbenzene product.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Aspects of the invention include catalysts, particularlyhydrodesulfurization catalysts, comprising: catalytic materialcomprising or consisting essentially of—i.e., having no more than 25,20, 15, 10, 5, 2.5, 1, 0.1, 0.001 wt % other metals than—molybdenum andcobalt, optionally as nanoparticles of molybdenum and/or cobalt; and acatalyst support comprising alumina; and (i) wherein the catalystsupport further comprises carbon nanofibers dispersed on a surface ofthe alumina, which nanofibers may have an average diameter in a range offrom 20 to 40, 22.5 to 37.5, 25 to 35, or 27.5 to 32.5 μm, and/or (ii)wherein the catalyst further comprises a dopant comprising boron, whichboron may be present in a range of from above 0 to 6, 1 to 5.5, 2 to5.25, 3 to 5.15, 3.5 to 5.1, or 4 to 5 wt % relative to total catalystweight, wherein the catalytic material is homogenously dispersed on thecatalyst support.

The catalytic material may comprise 12 to 18, 13 to 17, or 14 to 16 wt %of molybdenum, relative to the total catalyst weight, and/or 3 to 8, 4to 7, or 5 to 6 wt % of cobalt. A ratio of the Mo to Co may be in arange of from 10:1 to 1:1, 8:1 to 1.25:1, 7:1 to 1.5:1, 6:1 to 1.75:1,5:1 to 2:1, 4:1 to 2.25: 1, or 3:1 to 2.5:1. Useful lower and upperlimits of the Mo:Co ratio may be any of those in the preceding sentence,in any combination, and/or, for example, at least 1:1, 1.5:1, 2:1,2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.6:1, 2.75:1, 3:1, 3.25:1, 3.5:1, 3.75:1,4:1, 4.5:1, 5:1, or 6:1. Upper limits may be, for example 12:1, 9:1,7.5:1, 6.5:1, 6.25:1, or 5.5:1.

BET surface areas of catalysts within the scope of the invention may bein a range of from 150 to 230, 165 to 225, 180 to 220, 185 to 215, 190to 210, or 195 to 205 m²/g. Exemplary BETs may be at least 125, 135,145, 155, 160, 170, 175, 180, 182.5, 187.5, or 192.5 m²/g, and/or nomore than 232, 230, 222.5, 217.5, 212.5, 207.5, or 202.5 m²/g.

Catalysts of the invention may have (i) meso-pore surface areas in arange of from 165 to 185, 167.5 to 182.5, 170 to 180, 172.5 to 177.5, or173 to 176 m²/g; (ii) total pore volumes in a range of from 0.3 to 0.33,0.305 to 0.325, 0.31 to 0.323, or 0.315 to 0.320 cm³/g; (iii) averagepore diameters in a range of from 5 to 7, 5.1 to 6.9, 5.2 to 6.8, 5.3 to6.7, 5.4 to 6.6, 5.5 to 6.5, 5.6 to 6.5, or 5.75 to 6.25 nm; and/or (iv)hierarchy factors in a range of from 0.02 to 0.035, 0.0225 to 0.0325,0.023 to 0.032, 0.0235 to 0.0315, 0.024 to 0.031, 0.0245 to 0.0305,0.025 to 0.030, 0.0255 to 0.0295, or 0.026 to 0.029. Any of thesefeatures may be combined arbitrarily, e.g., (i) with (iv), (ii) with(iv), (i) with (iii), (i) with (ii) and (iv), (i) with (ii) and (iii),or (i) through (iv).

The catalytic material may comprise no more than 33, 20, 15, 10, 7.5, 5,4, 3, 2, 1, or 0.5 wt % of any of W and/or Ni, and/or even no more than33, 20, 15, 10, 7.5, 5, 4, 3, 2, 1, or 0.5 wt % of any metal besides Moand Co, and/or no more than 33, 20, 15, 10, 7.5, 5, 4, 3, 2, 1, or 0.5wt % of sulfur-as synthesized and/or outside of operational conditions.

Aspects of the invention provide methods of hydrodesulfurizing a firstmixture comprising an organosulfur, the method comprising: contactingthe first mixture with any catalyst(s) within the scope of the inventionin the presence of hydrogen gas, thereby forming a second mixturecomprising less sulfur than the first mixture, wherein the contacting iscarried out at a temperature in a range of from 250 to 350, 260 to 340,275 to 325, 280 to 320, 285 to 315, 290 to 310, or 295 to 305° C. for upto 10, 9, 8, 7, or 6 hours, i.e., 1 to 7, 2 to 6.5, 4 to 6.25, or 5 to 6hours, and a hydrogen gas partial pressure in a range of from 50 to 60,52.5 to 57.5, 53 to 57, or 53.5 to 56.5 bar-a. Inventive methods may beones in which the first mixture is contacted with the hydrogen gas for 5to 6 hours, and a ratio of an organosulfur concentration in the secondmixture to the organosulfur concentration in the first mixture is in arange of from 1:10 to 1:100000, 1:25 to 1:10000, or 1:50 to 1:1000. Atotal reduction of organosulfur content in the fuel may 90, 92.5, 95,97.5, 98, 99, 99.5, 99.9, 99.95, or 99.99 wt %, or even all detectableamounts, after 6 hours at 300° C. under 50 bar-a H₂, with no more than10, 8, 7.5, 7, 6, 5, 4, 3, 2.5, 2, 1, or even 0.5 wt % catalyst pertotal reaction mixture.

Aspects of the invention provide reactor systems, comprising: a vesselwith an internal cavity that contains inventive catalyst(s) as describedherein, wherein the vessel comprises (a) a hydrogen inlet configured todeliver hydrogen gas to the internal cavity, and (b) a feed inletconfigured to deliver a sulfur-containing mixture to the internalcavity; a stirrer configured to stir the catalyst and thesulfur-containing mixture in the presence of the hydrogen gas; a firststorage tank located upstream of the vessel and fluidly connected to thehydrogen inlet, wherein the first storage tank delivers the hydrogen gasto the hydrogen inlet; and a second storage tank located upstream of thevessel and fluidly connected to the feed inlet, wherein the secondstorage tank delivers the sulfur-containing mixture to the feed inlet,wherein the sulfur-containing mixture is contacted with the catalyst inthe presence of the hydrogen gas to form a desulfurized mixture.

Catalysts according to the invention are most preferably used with asupport, particularly one containing alumina, particularly γ-Al₂O₃.Useful supports may include, for example, at least 50, 60, 75, 85, 90,or 95 wt % alumina. The amount of alumina in the inventive catalysts maybe at least 15, 20, 25, 33, 40, 50, 60, 70, or 75 wt %, relative to thetotal catalyst weight. Catalysts within the scope of the inventiongenerally include, as metals, molybdenum (Mo) and cobalt (Co), and mayinclude further optional metals, such as tungsten (W), nickel (Ni),ruthenium (Ru), and/or rhodium (Rh). Catalysts within the invention mayexclude any or all of the optional metals, or may contain no more than10, 7.5, 5, 2.5, 2, 1, 0.5, 0.1, 0.001, or 0.0001 wt % or no more thantrace detectable amounts of any or all of the optional metals (i.e., W,Ni, Ru, and/or Rh) or any other metals, e.g., Fe, Cu, Pd, Pt, Re, Zn,Ag, Au, etc., beyond Mo and Co. Catalysts according to the inventiongenerally include no more than 25, 20, 15, 10, 5, 4, 3, 2, 1, 0.5, 0.1,0.001, or 0.0001 wt % or no more than trace detectable amounts ofsulfur, at least in synthesis of the catalysts. Carbon nanostructurespreferred in the invention may be nanofibers, rather than hollow tubes,even if this may sacrifice specific surface area in some circumstances.For example, the number of tube structures included in the carbonnanostructures may be fewer than 50, 33, 25, 20, 15, 10, 7.5, 5, 2.5, 2,1, or 0.1 wt %, relative to all carbon nanostructures in the catalyst.Likewise, the catalysts generally contain less than 15, 10, 7.5, 5, 2.5,2, 1, 0.1, 0.01, 0.001, or 0.0001 wt % cellulose or other carbohydrates.

The types of fuels relevant to hydrodesulfurization using one or morecatalysts according to the invention are generally not limited, but mayinclude, for example, refined and/or partially refined products (petethers, gasoline, diesel, kerosene, jet fuel, ethane, propane, butane,isobutane, pentane, hexane, heptane, octane, nonane, decane, undecane,dodecane, tridecane, tetradecane, pentadecane, hexadecane, isomers andunsaturated homologs of these, etc.), mineral oil, raw pyrolysisgasoline (RPG), hydrotreated pyrolysis gasoline, reformate, heavyaromatics, jet oil, atmospheric gas oil, residue fluid catalyticcracking (RFCC) gasoline, fluid catalytic cracking (FCC) gasoline, lightcracked naphtha, RFCC heavy naphtha, FCC decanted oil, vacuum gas oil,coker gas oil, coker diesel, coker naphtha, heavy and reduced petroleumcrude oil, petroleum atmospheric distillation bottom, petroleum vacuumdistillation bottom, asphalt, bitumen, tar sand oil, shale oil,liquid/solid products obtained by coal liquefaction or coal carbonationincluding coal tar, tar oil, light cycle oil (LCO), phenolic oil, lightanthracene oil, heavy anthracene oil, and pitch, Fischer-Tropschproducts, waxes, wood carbonation derivatives such as wood tar, hardwoodtar, resinous tar, and any combinations of two or more of any of these.

Incipient wetness impregnation, typically carried out in aqueoussolution, is the most common method of catalyst preparation, but leastcontrolled by adsorption. Generally, a support is impregnated with aprecursor-containing solution and dried. Metal salts used as catalystprecursors are dissolved in the impregnating solution, the volume ofwhich is made to match the pore volume of the support. The metal loadingis controlled by the concentration of metal ions in solution, which maymean that the support surface plays an insignificant role, merely actingas a physical support. The dry product is then further treated throughactivation treatments (e.g. calcination and/or reduction) to obtain thedesired catalyst.

Activity of boron-doped CoMo catalysts supported on γ-Al₂O₃, can bemodified, based on the amount of boron relative to the total catalystweight. AlMoCoB0%, AlMoCoB2%, and AlMoCoB5% were prepared through anincipient wetness impregnation method. As used herein, AlMoCox %indicates MoCo catalysts supported on γ-Al₂O₃, where x is the boronpercentage of the total catalyst weight. The results unexpectedlyindicated that AlCoMoB5% had the best performance in HDS ofdibenzothiophene (DBT).

Aspects of the invention may combine alumina with other supportmaterials, e.g., activated carbon, zeolite, alternate alumina morphology(e.g., α-Al₂O₃, γ-Al₂O₃), carbon structure, nanoporous carbon,mesoporous carbon, zirconia, titania, and/or silica, to tailor thepositive characteristics of combined system components.

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views.

The steps in preparing the Al—CNF—MoCo catalyst are depicted in FIG. 1,involving loading γ-Al₂O₃ with MoCo metals, with carbon nanofibers(CNF), or without CHF for comparison. The catalysts prepared can becharacterized structurally and morphologically by BET N₂ physisorption,temperature-programmed reduction (TPR) powder X-ray diffraction (XRD),scanning electron microscope (SEM), infrared spectroscopy (FT-IR), andthermogravimetric analysis (TGA), as exemplified in the drawings.

FIG. 2A provides N₂ adsorption-desorption isotherm curves of Al—MoCo andAl—CNF—MoCo prepared as disclosed in Example 1 below. The isothermcurves of both catalysts resemble a type IV isotherm withmicro/mesopores contributing to adsorption-desorption processes. As seenin FIG. 2A, the N₂ uptake at low relatively pressure indicates amicroporous nature of the material, while the hysteresis loop at highvalues of relative pressure indicates a mesoporous topography in thecatalysts prepared. As shown in FIG. 2A, the quantity adsorbed-desorbedby Al—CNF—MoCo at any relative pressure is higher than the quantityadsorbed-desorbed by Al-MoCo.

Table 1, below, sets forth textural properties of the Al—MoCo andAl—CNF—MoCo catalysts. In Table 1, it can be observed that theAl—CNF—MoCo catalyst has higher mesopore surface area, micropore surfacearea, total-pore volume, and micropore volume than the Al—MoCo catalyst.

TABLE 1 S_(BET) S_(Meso) S_(Micro) V_(micro) V_(total) Avg. PoreHierarch. Catalyst (m²/g) (m²/g) (m²/g) (cm³/g) (cm³/g) Diam. (nm)Factor Al—MoCo 166 155 11 0.0044 0.3055 7.15 0.013 Al—CNF—MoCo 200 17723 0.0096 0.3179 6.24 0.027

FIG. 2b depicts the pore size distribution of the Al—CNF—MoCo andAl—MoCo catalysts synthesized in Example 1. FIG. 2B indicates that bothcatalysts have a mesoporous character with close dominant pore diametervalues of 6.24 and 7.15 nm, respectively. These results indicate that,surprisingly, the addition of CNF to the catalysts enhances most of theAl—MoCo textural properties without severely sacrificing the averagepore diameter.

For investigating the effects of modification with CNF on the catalysttextural properties, a Hierarchical Factor (HF) for both materials wascalculated using Equation 1:

HF=(V _(micro) /V _(total))*(S _(meso) /S _(BET))   Eq. 1.

By substituting the textural parameter values into the Equation 1, HFvalues may be obtained for Al—MoCo and Al—CNF—MoCo, as seen in Table 1.These results show that Al—CNF—MoCo has a higher HF value than Al—MoCo,indicating that that Al—CNF—MoCo may have a higher adsorptionefficiency. The higher N₂ quantity adsorbed-desorbed by Al—CNF—MoCo atany relative pressure than Al—MoCo, noted above and seen in FIG. 2A,supports the HF conclusion.

FIG. 3 discloses H₂-temperature-programmed reduction (TPR) study of thereduction potential of metal oxides supported on Al—CNF or aluminaalone. FIG. 3 displays the H₂-TPR profiles of the Al—MoCo and theAl—CNF—MoCo catalysts prepared as described below in Example 1. As seenin FIG. 3, these Al—MoCo and the Al—MoCo—CNF catalysts show reductionpeaks of H₂ within the temperature range of from 420 to 530° C. and areduction peak in a range of from 660 to 700° C. The first two peaks inFIG. 3 can be assigned to the reduction of Mo polymeric octahedralstructures, i.e., Mo⁶⁺ to Mo⁴⁺. The higher temperature reduction atroughly 660° C. can be assigned the reduction of Mo⁴⁺to Mo⁰ in thepolymeric octahedral, tetrahedral, and bulk molybdena species. Thereduction temperatures for the Al—CNF—MoCo catalyst was indicated to belower than that of Al-MoCo in both regions. The lower and highertemperature reductions of Mo are presented below in Table 2.

TABLE 2 Temp. at Quantity Peak Peak Max. (cm³/g Concentration Catalyst(° C.) STP) (%) Al-CNT-MoCo 413.6 3.84 0.0604 496.2 3.52 0.053 738.933.05 0.156 Al—MoCo 435.7 3.67 0.0509 530.5 8.76 0.1549 696.7 10.130.1146

The increase in the reduction temperatures correlates to stronginteraction of the metal to the support, decreasing the dispersion, andthus, affecting the performance of the catalysts. These structuralindications are supported by the SEM images of the Al—CNF—MoCo catalystindicating well dispersed MoCo on the CNF. As shown in Table 2, the peaklocations at the lower temperatures for the Al—CNF—MoCo catalyst havelower values than Al—MoCo, meaning that Al—CNF—MoCo has lowermetals-to-support interactions than Al—MoCo. Accordingly, theAl—CNF—MoCo catalyst may have better metal dispersion on supports,particularly alumina and CNF-modified alumina, which may increase HDScatalytic activity.

FIG. 4 shows XRD patterns of the CNF and Al—CNF—MoCo and Al—MoCocatalysts prepared according to the method in Example 1 aftercalcination at 350° C. The XRD pattern of the CNF exhibits a predominantgraphite (002) diffraction peak around 26°. The CNF also shows (100) and(101) reflections in the region between 42° and 45° and a low intensity(004) line near 55°. The diffraction pattern of Al—MoCo showscharacteristic peaks of alumina and MoCo, confirming the presence ofCoMoO_(x) (JCPDS 00-021-868), and crystalline molybdenum oxide (JCPDS01-072-0527). The presence of cobalt and molybdenum oxides affords apeak at 26.6°, attributable to monoclinic CoMoO₄. Characteristic peaksat 20=34°, 39°, 46.5°, and 66° are likewise attributable to MoCo, andthe XRD pattern of the Al—CNF—MoCo catalyst shows characteristic CNFpeaks. A clear difference between the XRD patterns of Al—MoCo andAl—CNF—MoCo is the graphite (002) diffraction peak at ˜26°, whichslightly overlaps with the Al peak at 26.6°, which indicates asuccessful embedding of CNF within the alumina support.

The morphologies of the Al—CNF—MoCo catalysts prepared according to themethod in Example 1, and their elemental compositions, were investigatedby scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX)spectroscopy, as seen in FIG. 5A through D. The morphology of theAl-CNF-MoCo catalyst powder exhibits a small amount of carbon fibers,confirming the presence of CNF with a diameter of about 300 nm. Theaverage diameter of these CNF tube will vary depending upon desiredapplication, but, for example, may be anywhere in a range of from 10 nmto 1 μm, or 50 to 750 nm, 100 to 600 nm, 150 to 500 nm, 200 to 400 nm,250 to 375 nm, or 275 to 333 nm. Average CNF lengths, while notnecessarily limited, may be a range of from 0.1 to 50, 0.5 to 40, 1 to30, 1.5 to 20, 1.75 to 15, 2 to 10, 2.25 to 7.5, or 2.5 to 5 μm. The SEMimages in FIG. 5A to C also show uniformly distributed metalnanoparticles on the Al-CNF composite support surface, which may helpminimize agglomeration. The CNFs may provide a high and/or adjustablesurface area relative to alumina alone, and the surface area may allowdispersion of metal nanoparticles so as to increase the available activesites on the catalysts prepared. EDX analysis of the Al—CNF—MoCocatalysts, seen in FIG. 5D, indicate the elements Al, O, and C, due tothe use of the Al—CNF composite support, as well as the presence of thecatalyst metals, Mo (13.52 wt %) and Co (4.83 wt %).

FIG. 6 shows the FT-IR spectra of the Al—CNF—MoCo and Al—MoCo catalystsfrom Example 1, which likewise indicate the expected functional groupsof the catalysts. The broad band around 550 to 870 cm⁻¹ in FIG. 6 can beattributed to symmetric and asymmetric MoO terminal stretches. Thecharacteristic bands observed in the FT-IR spectrum of Mo═O at ˜988,878, and 634 cm⁻¹ may be ascribed to central vibrational modes of Mo═O.The dominant band at ˜820 cm⁻¹ is related to the vibration of Mo—O—Mobridging bonds. There could be an overlap of the characteristic peaks ofMo═O with that of the alumina which appeared at ˜741 cm⁻¹ and ˜641 cm⁻¹(Al—O bands). The broad bands at 550 to 900 cm⁻¹ indicate that MoCo washighly dispersed on the alumina. In the upper FT-IR spectrum in FIG. 6,i.e., the FT-IR of AlMoCo, the broad band at 3400 cm⁻¹ indicates thepresence of —OH groups on the alumina surface, as an —OH stretching bandof —Al—OH, and the band at 1637 cm⁻¹ can be attributed to —OH bending.After doping with CNF, bands appear at 2920 and 2850 cm⁻¹ for asymmetricand symmetric —CH₂— stretching vibrations in the CNF.

In reference to FIG. 7, thermal stability is an important factorindicative of the utility of HDS catalysts at high temperatures. The TGAcurves of Al-MoCo and Al-CNF-MoCo indicate that both have a good thermalstability, and Al—MoCo's thermal stability is not affected byintroducing CNF. The curves in FIG. 7 show a sharp weight loss below250° C. for Al—CNF—MoCo (10 wt %) and Al—MoCo (13.5 wt %), which may beascribed to the desorption of the absorbed moisture. The evaporation ofthe water molecules occurs at low temperatures, as shown in the TGAcurves, since H₂O binding with the supports in Example 1 is weak. Mostof this water is bound in an OH form which matches with the IR spectrumshowing the presence of the OH group on the catalysts prepared.Remaining weight loss for both catalysts occurred in a temperature rangeof 250 to 750° C., associated with the decomposition of residualprecursor(s). Surprisingly, according to the TGA curves, thedecomposition rate of Al—MoCo is faster than the correspondingdecomposition rate of Al—CNF—MoCo under the same testing conditions.FIG. 7 indicates that Al—CNF—MoCo catalysts have a unexpectedly superiorthermal stability to Al—MoCo catalysts. Without wishing to be bound toany specific theory, it is believed that the unexpectedly superiorthermal stability can be attributed to the presence of CNF as aco-support in the Al—CNF—MoCo catalysts.

FIG. 8 presents a chart of sulfur removal as a function of the HDSreaction time for the catalysts from Example 1. The desulfurizationreaction charted in FIG. 8 models Al—CNF—MoCo and Al—MoCo catalyticactivity in HDS of a model fuel comprising dibenzothiophene (DBT) in adecalin solvent. The reaction conditions were 55 bar H₂ partial pressureat 300° C. with stirring at 180 rpm, using 0.5 g of catalyst in 100 mLof the model fuel. FIG. 8 shows better catalytic performance forAl—CNF—MoCo at each reaction time interval compared to the Al—MoCocatalyst. After 6 hours of reaction at a constant temperature, 300° C.,the Al—CNF—MoCo catalyst reduced the sulfur content down to ˜7 ppm(˜1.273% of the original 550 ppm-S), below present regulatoryrequirements, while the Al—MoCo catalyst desulfurized only to 78 ppm. In6 hours reacting under similar or identical conditions, Al—CNF—MoCocatalysts within the scope of the invention may reduce the amount ofsulfur, i.e., end ppm-S/original ppm-S, to no more than 15, 10, 7.5, 5,4, 3, 2.5, 2, 1.5, 1.25, 1, 0.75, 0.5, 0.25, or even 0.1% or theoriginal amount.

Known important factors in the catalytic activity of HDS catalysts aretextural properties. HDS of DBT is believed to generally occur inmesoporous structures, i.e., containing pores with diameters between 2and 50 nm (or macroporous structures, with pore diameters above 50 nm),rather than in microporous structures, i.e., containing pores withdiameters less than 2 nm, since the DBT is a relatively large molecule.The mesoporous surface area of the Al—CNF—MoCo catalyst of Example 1 was177 m²/g, while that of the Al—MoCo catalyst was 154 m²/g at the samemetal loading, which indicates that the increase in the surface areacould be due to the CNF-doping. Typically useful mesoporous surfacesareas of CNF-modified may be in a range of from 155 to 200, 160 to 190,165 to 185, or 170 to 180 m²/g, though such surface areas are notnecessary to the function of inventive catalysts. Theadsorption-desorption efficiency of Al-CNF-MoCo also appears better thanthat of Al—MoCo, as indicated by the adsorption/desorption isotherms(e.g., FIG. 2A) and the HF calculations in Table 1. Notably, CNF appearsto improve the surface characteristics of γ-Al₂O₃ support, leading to ahigher efficiency and/or throughput in the HDS process of Al—CNF—MoCoversus Al—MoCo catalysts. Textural characteristics, including highersurface area and/or greater pore volume, may lead to improved metaldispersion on Al—CNF supports compared to alumina supports. Improvedmetal dispersion on the support is indicated by the TPR analysis in FIG.3, which metal dispersion in turn enhances the catalytic activity of thecatalyst.

In reference to FIG. 9, there are two main reaction mechanisms for theHDS process of DBT, namely, the hydrogenolysis pathway (DDS) and thehydrogenation desulfurization (HYD) pathway. In the DDS mechanism,sulfur is removed by H₂, without reducing the DBT aromatic rings. In theDDS pathway, the removal of sulfur by direct C—S bond hydrogenolysisproduces biphenyl (BiPh), which can be the predominant organic productin this pathway. Subsequently, the biphenyl can be hydrogenated toproduce cyclohexylbenzene (CHB). In the HYD mechanism, the DBT aromaticrings are first hydrogenated and then the reduced compound isdesulfurized. In contrast to DDS, hexahydrodibenzothiophene (HHDBT)or/and tetrahydrodibenzothiophene (THDBT) are the intermediate productsof the main reaction in the HYD pathway mechanism. These HYDintermediates are desulfurized to give the same secondary product asDDS, i.e., cyclohexylbenzene (CHB). In both mechanisms, bicyclohexyl(BiCh) is formed in trace amounts, which is the result of thehydrogenation of the CHB in a slow pattern. FIG. 9 illustrates possiblereaction mechanism for the HDS of DBT over the Al—CNF—MoCo catalysts.

In reference to FIG. 10A to C, GC-MS was conducted on reaction mixturesamples to analyze the mechanism of the HDS over the Al—CNF—MoCocatalyst. Peaks corresponding to the HDS of DBT are shown in FIG. 10A.The GC-MS peaks for the HDS products shown in FIG. 10A are complex, withroughly 500 compounds are separated in every run. Mass spectra of twopeaks, respectively corresponding to biphenyl and bicyclohexyl, areshown in FIG. 10B and C. The results in FIG. 10A to C indicate that HDSover the Al—CNF—MoCo catalysts follow a DDS reaction mechanism.

FIG. 11A and B show an exemplary HDS reaction system, which may includeone or more reactors, hydrogen gas suppliers, pumps, gas compressors,valves, and/or fuel tanks. Liquid fuel with sulfur content may pumpedinto the reactor, containing the HDS catalysts, and known arrangementsmay be alternatively or additionally used for gaseous and/or fluidizedfuel(s). Hydrogen gas (H₂) is injected into the reactor at a desiredflow rate or partial pressure. The fuel and hydrogen flow rates maycontrolled using the valves, and the reaction temperature may beadjusted, e.g., increased, using a reactor heating jacket or other knownheating and/or cooling units. The reaction mixture may stirred, shaken,or otherwise agitated in the reactor, e.g., by an overhead rotator, toensure good contact with the catalysts. Optional baffles and variousstirring shapes are not show for simplicity, though these may be chosenfreely (e.g., hook, bowtie, paddle, dual paddle, ribbon, turbine vortex,umbrella type, flat turbine type, anchor, spiral propeller, ruvastarcyclo, dispersing homogenizing, open, high shear reverse flow, and/orhigh shear homogenizer type blades may be useful, as may be, onrelatively small scales, magnetic stirrers) based upon the viscosityand/or mixing requirements of the reaction mixture. The HDS reactiongenerally occurs at high temperature and pressure in a controlled and/orclosed environment. The treated fuel may be subsequently withdrawn fromthe reactor. A recycle line may be added to the HDS system, as shown inFIG. 12. Some the reactor outputs can be separated and recycled to thereactor by mixing or distributed valves. A goal of the recycle line maybe to have a more dynamic system which allows the desirable levels ofsulfur removal from the fuels, particularly liquid fuels.

The results of the hydrodesulfurization (HDS) reactions usingCNF-modified catalysts demonstrates that doping alumina with carbonnanofiber may enhance the desulfurization of dibenzothiophene relativeto Al—CoMo, using an Al—CNF—MoCo catalyst as described herein. BETanalysis of Al—CNF—MoCo catalysts indicates that introducing CNF as aco-support can enhance certain textural characteristics of MoCocatalysts, including the surface area, pore size, and the HF factor.These influenceable textural characteristics indicate potential toenhance catalytic efficacy. Thus, Al—CNF—MoCo catalysts within the scopeof the present invention, can reduce sulfur levels inhydrocarbon-containing fluids to below tolerated levels, even betterthan Al—CoMo catalysts without CNF modification, and, thus, may beuseful for desulfurization on laboratory, pilot plant, and industrialscale.

FIG. 13 depicts a laboratory preparation of boron-modifiedMoCo-on-alumina HDS catalysts, which is detailed below in Example 2.FIG. 14 shows a setup for evaluating HDS activity of the catalysts usinga batch reactor from Parr Instrument Company, Model 4848B, asimplemented herein for HDS experiments in Example 2.

FIG. 15 discloses the physical adsorption/desorption isotherms of N₂ at−196° C. for the catalysts prepared in Example 2. Type IV isotherms areindicated for all the catalysts made in Example 2 indicating thepresence of the mesoporous structures in the catalysts. Table 3, below,summarizes the textural properties of the optionally boron-modifiedcatalysts from Example 2, including BET surface area, mesopore surfacearea, micropore surface area, micropore volume, total pore volume,average pore volume, and hierarchical factor (HF). In Table 3, thesurface areas and micropore volume were calculated by t-plot, d_(p)represents the adsorption average port width (4V/A) using the BJHmethod, and “HF” represents the Heirarchical Factor calculated usingEquation 1 as above.

TABLE 3 S_(BET) s_(meso) s_(micro) V_(micro) V_(total) d_(p) Catalyst(m²/g) (m²/g) (m²/g) (cm³/g) (cm³/g) (nm) HF AlMoCoB0% 155 135 20 0.0040.138 6.1 0.003 AlMoCoB2% 176 154 22 0.008 0.305 6.6 0.004 AlMoCoB5% 206165 41 0.019 0.306 7.2 0.012

As seen in Table 3, the boron-doped γ-Al₂O₃ samples showed higher BETsurface area values than the BET surface area of the unmodified sample,i.e., AlMoCoB0%. The BET surface area was observed to increase with thepercentage boron, which is believed to indicate good dispersion of boronnanoparticles on the catalyst. The mesoporous surface area of AlMoCoB0%,AlMoCoB2%, and AlMoCoB5% from Example 2 were determined to be 135, 154,and 165 m²/g, respectively. The mesoporous surface area can affect HDScatalytic activity, but the role of boron-modification was surprisinglyfound to eventually result in lesser activity, beyond 5 wt %. Withoutwishing to be bound to any theory, it is believed that boron canagglomerate on the catalysts, leading to less surface area and,consequently, lower HDS performance. Surprisingly then, of the catalystsprepared in Example 2, AlMoCoB5% had the best HDS catalytic performance.

In reference to FIG. 16A, the boron-modified catalysts of Example 2 weresubjected to H₂-TPR, i.e., temperature-programmed reduction, to studythe interaction between the boron-modified MoCo species and thesupporting materials. Particularly, H₂-TPR was used to characterize thereduction of the boron-modified MoCo species on the catalyst surface byH₂. FIG. 16A shows H₂-TPR profiles of the AlMoCB0%, AlMoCB2%, andAlMoCB5% catalysts, each having one predominant H₂ reduction peak withinthe temperature range of 525 to 560° C. and another reduction peakwithin the temperature range of 700 to 770° C. At a relatively lowtemperatures, 520 to 560° C., the main H₂ consumption temperature,corresponding to the Mo⁶⁺ to Mo⁴⁺ reduction of polymeric octahedral Mo,is observed. The reduction temperature of H₂ between 700 and 770° C.,may be attributed to the Mo⁴⁺ to Mo⁰ reduction of polymeric octahedral,tetrahedral, and bulk molybdena species.

The temperature of the reduction peaks in the H₂-TPR profiles of FIG.16A reflects the strength of the interaction between the active metalcomponents and the support in the catalysts from Example 2. Increases inthe reduction temperature are believed to indicate increases in themetal-support interaction, which can decrease dispersion and affectcatalytic performance. As seen in Table 4, the peak locations at a lowtemperature of the boron-modified MoCo catalysts have the lower valuesthan the undoped AlMoCoB0%, meaning that the boron-containing specieshave less strong metal-to-support interaction. Thus, boron-dopedcatalysts may have better metal dispersion, and better HDS catalyticactivity.

TABLE 4 Temp. at Quantity Peak Peak Max. (cm³/g Conc. Catalyst (° C.)STP) (%) AlMoCoB0% 558 6 0.118 770 4 0.06 AlMoCoB2% 551 17 0.361 702 330.283 AlMoCoB5% 526 21 0.352 695 34 0.29

In reference to FIG. 16B, the surface acidity characteristics ofcatalysts prepared in Example 2 were determined byNH₃-temperature-programmed desorption (TPD). The acidity observed inAlMoCoB0% catalyst is moderate, characterized by Lewis acid sites in thetemperature ranges of 160 to 175° C. and 490 to 520° C. Theboron-modified catalysts, AlMoCoB2% and AlMoCoB5%, exhibit greatersurface acidity than AlMoCoB0%, as shown in FIG. 16B and Table 5, below.The boron doping on the Al-MoCo appears to enhance the surface acidityof the catalysts, based on increased areas under the curves in FIG. 16B.

TABLE 5 Temp. at Quantity Peak Peak Max. (cm³/g Conc. Catalyst (° C.)STP) (%) AlMoCoB0% 173 4.57 0.011 513 5.39 0.0107 804 0.17 0.003AlMoCoB2% 177 2.64 0.0058 503 4.03 0.0064 751 6.41 0.0188 AlMoCoB5% 1752.97 0.0061 485 5.88 0.0074 784 8.28 0.0253

The x-ray diffraction (XRD) patterns of the catalysts prepared inExample 2 are shown in FIG. 17A to C. The XRD patterns of the AlMoCoB0%in FIG. 17A exhibits peaks at 20=26.6°, 45.5°, and 67.1° which arisefrom crystalline phases of γ-Al₂O₃. The XRD pattern of 2 wt %boron-doped Al-MoCo is illustrated in FIG. 17B, and the XRD pattern of 5wt % boron-doped Al—MoCo is illustrated in FIG. 17C. The intensities ofnanomaterial peaks (2θ=26.6° are known to decline by metal loading. Theintensities of nanomaterial peaks increase as the weight percentage (%)of boron increases on supported catalysts. FIG. 17B shows thediffraction peaks at 2θ=22.5° and 26.6° characteristic for catalysts ofcobalt and molybdenum loaded on an alumina support and doped with boronwith 2%. The intensities of the diffraction peak of Al₂O₃ (20=26.6° aregenerally more predominant than diffraction peaks from metalloid B andmetallic Co, especially for the catalysts with higher boron contents.Boron-doped Al—MoCo on alumina diffraction lines in FIG. 17C are seen at2θ=4.5°, 22.5°, 26.6°, 45.5°, and 67.5° are attributed to the (021),(040), and (110) crystallographic planes of the orthorhombic MoO₃ phase.The presence of broad Mo species peak indicates a small particle size.Peaks corresponding to Mo₃S₄ crystallite formations at 14.4° and 32.71°could not be assigned, and peaks from molybdenum oxide species haddecreased intensity. MoCo and boron indications are observable in theXRD spectra of FIG. 17B and C for AlMoCoB2% and AlMoCoB5%/γ-Al₂O3.

FIG. 18 shows the FT-IR spectra of the boron-modified MoCo catalystssupported on γ-Al₂O₃ from Example 2. The spectra of AlMoCoB2% andAlMoCoB5% exhibit Al-O stretching modes at 582 cm⁻¹, and symmetric andasymmetric Mo═O terminal stretches at 790 and 900 cm⁻¹, which are knownfor doped boron catalysts. After doping with boron, the symmetric andasymmetric Mo═O terminal stretches in doped boron catalysts shift togreater wavenumbers, i.e., 820 and 949 cm⁻¹ and the intensity of theband attributed to an Al-O stretching mode is weaker.

FIG. 19A to F show qualitative and quantitative characterizations of thecatalysts prepared in Example 2 using EDX analysis and SEM. As seen inFIG. 19A, Mo, Co, and O were detected as the main elements in theγ-Al₂O₃ support, indicating a synthesis of MoCo catalysts without anyother elemental impurities. In addition to MoCo, boron was detected inthe boron-doped MoCo catalysts, as shown in FIG. 19C and E, indicatingsuccessful loading of boron onto the γ-Al2O3 support in those catalyst.The quantitative reports indicate amounts of boron on the AlMoCoB2% andAlMoCoB5%, which were measured to be 1.96 wt % and 4.68 wt %,respectively. The chemical composition of the prepared metal catalystswas further analyzed using backscattered electron (BSE) and secondaryelectron (SE) analysis as seen in FIG. 19B, D, and F, with the resultsbeing tabulated in FIG. 19A, C, and E. As seen in FIG. 19C and E,AlMoCoB2% and AlMoCoB5% show a boron content error of 0.14 wt % sigmaand 0.29 wt % sigma, respectively.

FIG. 20 shows thermogravimetric analysis (TGA) graphas of AlMoCoB0%,AlMoCoB2% and AlMoCoB5% catalysts at a heating rate of 10° C./min, acooling rate of 30° C., and a temperature range of 25 to 800° C. The TGAcurves indicate that the main part of weight loss occurred between 25and 250° C., for AlMoCoB5% (˜12 wt %), AlMoCoB2% (˜12.7 wt %), andAlMoCoB0% (˜14 wt %). These losses are again attributed to thevaporization of the atmospheric moisture in and on the catalystsprepared. The remaining weight loss of ˜5% for each of the catalystsoccurs in a temperature range of 250 to 700° C., and is associated withthe decomposition of the residual precursor.

The HDS performance of the catalysts prepared in Example 2 was examinedconsidering the parameters of temperature, pressure, dosage, and contacttime. Central composite design was used to examine the influence of theparameters on the surface responses of the catalysts prepared witha >95% confidence level. Low and high levels of the parameters are shownin Table 6, and the plots obtained are depicted in FIG. 21A and B.Normal plots of effects indicate that the temperature, pressure, anddosage are the most influential factors, as shown in FIG. 21B. Byincreasing the reactor temperature and pressure, the efficiency alsoappears to be increased. Also, the efficiency increased by increasingthe dosage of the catalyst and contact time. Analyzing the combinationof the range of the “low” and “high” values on the efficiency, as inFIG. 21B with the AB interaction analysis, indicates that by increasingthe contact time and dosage, the performance would be increased.However, the efficiency levels off with further increase in both contacttime and dosage after an optimum dosage of 0.6 g and contact time of 6hours. Center points also appear to indicate satisfactory performance.

TABLE 6 Low Central point High Variable (−) (0) (+) (A) Temperature (°C.) 250 300 350 (B) Pressure (bar) 30 40 50 (C) Dosage (mg) 0.2 0.4 0.6(D) Contact time (h) 2 3 6

The HDS activity of the AlMoCoB0%, AlMoCoB2%, and AlMoCoB5% catalystsprepared in Example 2 are depicted in FIG. 22. In comparison, theactivities of AlMoCoB0% and AlMoCoB2% were roughly same, but asignificant enhancement in HDS activity was observed for AlMoCoB5%.Without wishing to be bound to any theory, it is believed that thewell-crystallized AlMoCoB5% structure has fewer —OH groups on itssurface, thus limiting the influence the metal-to-support interactionsand allowing the creation of more CoMoS species. The enhanced stackingof sulfided Al—MoCoB layers may shield the polarization of Al ions ofalumina to some extent, potentially disinhibiting Co on Mo and allowingincreased formation of CoMoS species and correspondingly increasing theHDS catalytic activity. As seen in FIG. 22, the boron-modified Al—MoCocatalysts within the scope of the invention are suitable to remove atleast 87.5% of all sulfur in the starting material fuel, akin to that inExample 1, within 6 hours of reaction time under the conditionsdescribed in Example 1. For example, the boron-modified Al-MoCocatalysts, particularly AlMoCoB5%, may be suitable to remove at least90, 92.5, 95, 96, 97, 97.5, 98, 98.5, 99, 99.5, 99.9, or all detectableorganosulfur by 6 hours of operation under the conditions discussedbelow.

As in the case discussed for the CNF-doped catalysts, thehydrodesulfurization (HDS) of dibenzothiophene (DBT) can occur via twoparallel pathways, illustrated in FIG. 23. The first pathway is thedirect desulfurization or hydrogenolysis by C—S bond cleavage in asingle step. The second pathway is hydrogenation in two or three stepsthrough the hydrogenation of one of the phenyl rings followed by C—Sbond cleavage. HDS of DBT via the direct desulfurization pathway yieldsbiphenyl and H₂S as the final products. However, the hydrogenationpathway results in the formation of intermediates, such astetrahydrodibenzothiophene and hexahydrodibenzothiophene, followed byfast desulfurization to form cyclohexylbenzene. The directhydrodesulfurization pathway consumes substantially less hydrogen. Thus,direct hydrodesulfurization is preferred.

GC-MS analysis was carried out to detect the products of HDS reactionproducts over AlMoCoB5% catalyst. Peaks corresponding to HDS of DBT areshown in FIG. 24A to D. As shown in FIG. 24A, the GC-MS chromatogram ofHDS reaction products indicates a complex mixtures, separating out some500 compounds in every analysis. FIG. 24B shows MS peaks correspondingto unreacted DBT in the analyzed sample. The important peakscorresponding to HDS products were again found to be in low abundances.However, GC peaks corresponding to biphenyl and cyclohexylbenzene wereidentified and their MS presented in FIG. 24C and D. The HDS reactionover AlMoCoB5% catalysts thus appears to proceed by the two parallelpathways, direct and indirect hydrodesulfurization reaction.

EXAMPLE 1

Materials: ammonium molybdate, (NH₄)₆Mo₇O₂₄.4H₂O, purity 98%; cobaltnitrate (Co(NO)₃.6H₂O, purity 98%, diethylene glycol, (HOCH₂CH₂)₂O,purity 99%; decalin, C₁₀H₁₈, purity 99%; dibenzothiophene (DBT), C₁₂H₈S,purity 98%; and ethanol, C₂H₆O, purity 99%, were all purchased fromSigma Aldrich. CNF was prepared by chemical vapor deposition (CVD)method which well-known method.

Synthesis 1: commercial alumina was heated to 500° C. for a heating timeof about 3 h to obtain γ-Al₂O₃. Some 9.5 g of γ-Al₂O₃ was mixed with 0.5g of carbon nanofiber (CNF) to obtain carbon nanofiber-doped γ-Al₂O₃using the sol-gel method. The mixture was mixed with 100 mL of deionizedwater, 10 mL ethanol, and 5 mL diethylene glycol, and stirred for 1hour. The mixture was refluxed at 110° C. for around 6 hours. Theresulting precipitate was separated and dried at 100° C., to give anAl—CNF composite. The Al—CNF composite was loaded with Mo nanoparticles(15 wt %) and Co nanoparticles (5 wt %), using incipient wetnessimpregnation. 80 mL of deionized water was added to 4.8 g of the Al—CNFcomposite under stirring at 85° C. for 35 minutes. Then, 100 mL ofaqueous solution of 1.66 g ammonium molybdate and 1.46 g cobalt nitratewere added to the dispersed alumina and kept under stirring at 85° C.for 3 hours. During the stirring, 5 mL of diethylene glycol was added toenhance the connection between the nanoparticles and the aluminasupport. The resultant mixture was separated and dried at 110° C. for 5hours. The prepared catalyst was then calcined at 350° C. This exemplarypreparation of Al-CNF-MoCo is illustrated in FIG. 1. The same method wasused to load γ-Al₂O₃ with MoCo metals, without doping with CNF, forcomparison. The prepared catalysts were characterized for structural andmorphological properties by BET N₂ physisorption, temperature-programmedreduction (TPR), powder X-ray diffraction (XRD), scanning electronmicroscope (SEM), infrared spectroscopy (FT-IR), and thermogravimetricanalysis (TGA).

Evaluation of the CNF-Modified Catalysts Prepared in Example 1: The HDSactivity of the Al—MoCo and Al—CNF—MoCo catalysts prepared in Example 1was separately evaluated using a batch reactor, Model 4848B, purchasedfrom the Parr Instrument Company.

The HDS was conducted at 300° C. and 55 bar H₂ partial pressure. Around0.50 g of the each Al—MoCo or Al—CNF—MoCo catalyst was inserted in thereactor vessel with 100 mL of a model fuel, containing dibenzothiophene(DBT) at an initial concentration of 550 ppm-S in decalin. When thereaction temperature reached 300° C., a first sample was collected andconsidered as the zero point. Thereafter, following each hour ofreaction at 300° C., a further sample was collected by a manual valve,and the reaction was monitored for 6 hours. The sulfur concentrations inthe collected samples were then analyzed by gas chromatography-massspectrometry (GC-MS) employing sulfur chemiluminescence detection(GC-SCD).

Example 2

Materials: ammonium molybdate, (NH₄)₆Mo₇O₂₄.4H₂O, cobalt nitrate,Co(NO₃)₃.6H₂O, boron trifluoride ethylamine complex, BF₃.C₂H₅NH₂,diethylene glycol, ethanol, were obtained from Fluka, anddibenzothiophene (DBT), C₁₂H₈S (purity 98%, MW 184.26 g/mol, d 1.25g/cm³), was obtained from Sigma Aldrich. Bicyclo[4.4.0]decane, i.e.,decahydronaphthalene or decalin, C₁₀H₁₈, (98% purity, MW 138.25 g/mol,d˜0.896 g/cm³), a colorless liquid was used as a solvent for DBT inpreparing model fuels, was obtained from Sigma Aldrich. High purity (18μS/cm) de-ionized water was used and obtained in-house usingThermoScientific Barnstead Nanopure after distillation with a LabstrongFiSTREEM™ II 2S Glass Still distiller.

Synthesis 2: alumina was loaded with Mo nanoparticles (15 wt %) and Conanoparticles (5 wt %), by incipient wetness impregnation. 7 g ofalumina was dispersed in 100 mL of deionized water under stirring at 80°C. for 20 minutes. Then, 50 mL of aqueous solution of ammoniummolybdate, (NH₄)₆Mo₇O₂₄.4H₂O, and cobalt nitrate, Co(NO₃)₃.6H₂O, wereadded to the dispersed alumina and kept under stirring at 80° C. for 110minutes. To dope the obtained composite with boron, 50 mL of aqueoussolutions of boron trifluoride ethylamine, BF₃.C₂H₅NH₂, were added tothe mixture under stirring at 80° C. for 3 hours. During the stirring,20 mL of diethylene glycol was added to enhance adhesion between thenanoparticles and alumina support. The resultant mixture was filteredand dried at 100° C., FIG. 13 illustrates this method. The filteredcatalyst was calcined at 400° C. for 3 hours under the flow of N₂ gas.Following the same procedures, alumina-supported CoMo catalysts weredoped with different boron percentages (0 wt %, 2 wt %, and 5 wt %) andthe final catalysts were labeled AlMoCoB0%, AlMoCoB2%, and AlMoCoB5%,where x % is the boron percentage on the catalyst. Initial resultsindicated that HDS adding more than 5% showed less HDS performance, soit was surprisingly found that the optimum boron doping on the catalystswas in a range of from 2.5 to 7.5, 3.5 to 5.5, 4 to 5 wt %, or close to5 wt %.

Evaluation of the Boron-Modified Catalysts Prepared in Example 2: TheHDS activity of the boron-modified catalysts was evaluated using a batchreactor, Parr Instrument Company Model 4848B. FIG. 14 schematicallydiagrams the system used for the boron-modified catalytic HDS reactions.The HDS reaction was conducted at 300° C. under 50 bar H₂ partialpressure. 0.6 g of a respective catalyst, AlMoCoB0%, AlMoCoB2%, andAlMoCoB5%, were inserted in the reactor vessel with 100 mL of the modelfuel, containing DBT at an initial concentration 650 ppm-S in decalin.Each test was conducted for 6 hours after achieving the target processconditions. When the reaction temperature reached 300° C., a firstsample was collected and considered as zero-hour sample. Thereafter,samples were collected every hour over 6 hours through a manual valve.The sulfur content in the model fuel and the samples were quantifiedusing a GC-SCD, with products identified by GC-MS.

Numerous modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

1. A hydrodesulfurization catalyst, comprising: catalytic materialcomprising a molybdenum oxide and a cobalt oxide; and a catalyst supportcomprising alumina; and wherein the hydrodesulfurization catalystsupport further comprises carbon nanofibers dispersed on a surface ofthe alumina; and wherein the hydrodesulfurization catalyst furthercomprises a dopant comprising boron in an amount such that the boron ispresent in a range of from 1 to 5.5 wt % relative to totalhydrodesulfurization catalyst weight, wherein the catalytic material ishomogenously dispersed on the catalyst support. 2-4. (canceled).
 5. Thehydrodesulfurization catalyst of claim 1, wherein the catalytic materialcomprises 12 to 18 wt % of molybdenum, relative to totalhydrodesulfurization catalyst weight.
 6. The hydrodesulfurizationcatalyst of claim 1, wherein the catalytic material comprises 3 to 8 wt% of cobalt, relative to total hydrodesulfurization catalyst weight. 7.(canceled)
 8. The hydrodesulfurization catalyst of claim 6, wherein themolybdenum and/or cobalt is present in the form of nanoparticles.
 9. Thehydrodesulfurization catalyst of claim 1, having a BET surface area in arange of 150 to 230 m²/g.
 10. The hydrodesulfurization catalyst of claim1, wherein the carbon nanofibers have an average diameter of 20 to 40μm.
 11. The hydrodesulfurization catalyst of claim 1, having a meso-poresurface area in a range of from 165 to 185 m²/g.
 12. Thehydrodesulfurization catalyst of claim 1, having a total pore volume ina range of from 0.3 to 0.33 cm³/g.
 13. The hydrodesulfurization catalystof claim 1, having an average pore diameter in a range of from 5 to 7nm. 14-16. (canceled)
 17. The hydrodesulfurization catalyst of claim 1,wherein the catalytic material comprises no more than 5 wt % of sulfur.18-20. (canceled)